The present invention relates generally to the reproduction of visual and audio information, and more particularly, is directed to a method and apparatus for substituting a higher quality audio signal recorded with the visual signal during reproduction of the latter.
When preparing motion pictures and the like for distribution, it is common practice to edit, dub, and make copies of the original. As a result, copies are made from copies of the original visual picture information and audio soundtrack. The sound in these multiple generation copies, however, loses fidelity in making the final film or video tape. For example, a seventh generation audio signal may eventually be used in the final version of the distributed film. This clearly is undesirable. Specifically, a seventh generation audio signal may have a signal to noise ratio of 30 db and a frequency response of 50 Hz-9 kHz, while a first generation audio signal recorded on a compact disc may have a signal to noise ratio of 96 db and a frequency response of 0 Hz-20 kHz.
One problem with substituting the higher quality audio signal for the final release audio signal is that of providing synchronization between the two audio signals, and thereby providing synchronization between the higher quality audio signal and the moving picture signal. This is because there is a lack of compatibiilty between different synchronization systems, particularly when different recording media are used. For example, a distributed motion picture may be recorded on film, and the higher quality audio signal may be recorded on a compact disc.
In this regard, the applicant herein has become aware of the following references.
U.S. Pat. No. 4,433,351 discloses a system which automatically adjusts the phase relation between signals reproduced from different tracks of the same magnetic tape, to be equal to the phase relation of the original signals, by adjusting rotation of the playback head. In this system, the two reproduced signals are supplied to zero crossing detectors, which supply outputs to monostable multivibrators. The outputs of the monostable multivibrators are supplied to a flip-flop circuit, the output of which is used to control the rotation of the playback head to adjust the phase relation between the signals.
U.S. Pat. No. 3,831,192 discloses a frequency deviation compensation system in which a pilot signal and information signal are both reproduced from the same tape. The signals are then supplied to zero crossing detectors, and the output from the zero crossing detector supplied with the pilot signal is compared with an oscillation signal. Dependent upon the frequency deviations detected in the pilot signal, pulses are added or subtracted from the pulses produced in response to the information signal. As a result, a utilization device is controlled, based upon an accumulation of overflow or underflow pulses.
U.S. Pat. No. 4,414,587 discloses a skew sensing apparatus for digital tape playback, in which digital data recorded on two tracks of the same tape is reproduced and supplied to parity bit lock-on circuits, which produce word clock signals in response thereto. These latter signals are supplied to a phase detector which detects the phase difference between the signals and adjusts the skew in response thereto.
U.S. Pat. No. 4,422,109 discloses a device for adjusting a magnetic recording/reproducing apparatus, based on the optimum bias of each magnetic tape that is used therewith. In this regard, the device uses a test signal which is recorded on and reproduced from the tape.
U.S. Pat. No. 4,559,569 discloses a circuit arrangement for correcting frequency response in view of the frequency response of a sound field.